1. Field of the Invention
The present invention relates to the field of electric power consumption measurement in general and, in particular, to an electronic watthour meter which employs a magnetoresistive bridge sensor utilizing a ferromagnetic material such as permalloy.
2. Description of the Prior Art
The well-known electro-mechanical induction watthour meter has been utilized for measuring electric energy usage for the purpose of computing electric energy revenues for many years. Recently, however, added flexibility has been required of metering devices such as the utilization of variable rates, remote reading communication, instantaneous power consumption readings and other functions. Such new demands for flexibility have led to the increased need for a low cost, highly accurate and reliable watthour meter which is capable of performing diverse functions.
A magnetometer consisting of an anisotropic thin ferromagnetic film arranged in a Wheatstone bridge configuration utilized to sense an AC magnetic field is known in the prior art. An example of such measurement is disclosed in U.S. Pat. No. 3,546,579, which illustrates and describes the magnetometer utilizing such a bridge configuration. It is also known in the prior art that certain alloys of iron and nickel known as permalloy may be used to create very sensitive magnetoresistive elements. While sensitive magnetoresistive bridge configurations have found many uses, these have been primarily in sensing very small electric currents. The prior art has not shown how to take advantage of the high sensitivity of such elements to provide a simple, inexpensive system for measuring electric power consumption.